Peer-reviewed research and review articles

Pragmatic and structural constraints shaped the pedagogical choices volunteer educators made, as did their professional identification and comfort with engineering.

Youth programs implemented during out-of-school time often rely on volunteers. These volunteers are responsible for selecting and adapting curriculum and facilitating activities, so their pedagogical practices become primary contributors to program quality, and ultimately, youth outcomes. To describe volunteers' pedagogical practices, I conducted a qualitative case study at three sites where volunteer educators were implementing a design-based 4-H curriculum. The curriculum advanced youth scientific literacy by supporting scientific inquiry in conjunction with planning, designing and making shareable artifacts. Through detailed observations, videos and focus groups, I identified six common pedagogical practices, though educators differed widely in which ones they used. Pragmatic and structural constraints shaped their choices, as did their professional identification as engineers, or not, and their relative comfort with engineering. To support volunteer educators in implementing a learner-centered educational program, curricula designers might be more specific in recommending and explaining pedagogical practices, and program managers might better train volunteer educators in those preferred practices.

Sufficient rainfall and appropriate soil temperatures during the canola planting window occur statewide on average 1 in 3 years, but camelina is significantly more drought and cold tolerant.

In California, Brassica oilseeds may be viable crops for growers to diversify their cool-season crop options, helping them adapt to projected climate change and irrigation water shortages. Field trials have found germination and establishment problems in some late-planted canola, but not camelina at the same locations. We used computer modeling to analyze fall seedbed conditions to better understand this phenomenon. We found seedbeds may be too dry, too cold, or both, to support germination of canola during late fall. Based on seedbed temperatures only, canola should be sown no later than the last week of November in the Central Valley. Camelina has broader temperature and moisture windows for germination and can be sown from October to December with less risk, but yields of camelina are lower than canola yields. In areas without irrigation, growers could plant canola opportunistically when seedbed conditions are favorable and use camelina as a fallback option.

Analyses of cropland ownership patterns can help researchers prioritize outreach efforts and tailor research to stakeholders' needs.

Land ownership is one of the primary determinants of how agricultural land is used, and property size has been shown to drive many land use decisions. Land ownership information is also key to understanding food production systems and land fragmentation, and in targeting outreach materials to improve agricultural production and conservation practices. Using a parcel dataset containing all 58 California counties, we describe the characteristics of cropland ownership across California. The largest 5% of properties — with “property” defined as all parcels owned by a given landowner — account for 50.6% of California cropland, while the smallest 84% of properties account for 25% of cropland. Cropland ownership inequality (few large properties, many small properties) was greatest in Kings, Kern and Contra Costa counties and lowest in Mendocino, Napa and Santa Clara counties. Of crop types, rice properties had the largest median size, while properties with orchard trees had the smallest median sizes. Cluster analysis of crop mixes revealed that properties with grapes, rice, almonds and alfalfa/hay tended to be planted to individual crops, while crops such as grains, tomatoes and vegetables were more likely to be mixed within a single property. Analyses of cropland ownership patterns can help researchers prioritize outreach efforts and tailor research to stakeholders' needs.

Remote-sensing modeling produces an accurate regional salinity map of the western San Joaquin Valley, useful for growers and state agencies.

Soil salinity negatively impacts the productivity and profitability of western San Joaquin Valley (WSJV) farmland. Many factors, including drought, climate change, reduced water allocations, and land-use changes could worsen salinity conditions there, and in other agricultural lands in the state. Mapping soil salinity at regional and state levels is essential for identifying drivers and trends in agricultural soil salinity, and for developing mitigation strategies, but traditional soil sampling for salinity does not allow for accurate large-scale mapping. We tested remote-sensing modeling to map root zone soil salinity for farmland in the WSJV. According to our map, 0.78 million acres are salt affected (i.e., ECe > 4 dS/m), which represents 45% of the mapped farmland; 30% of that acreage is strongly or extremely saline. Independent validations of the remote-sensing estimations indicated acceptable to excellent correspondences, except in areas of low salinity and high soil heterogeneity. Remote sensing is a viable tool for helping landowners make decisions about land use and also for helping water districts and state agencies develop salinity mitigation strategies.

In a seeding study in the California foothills, annual ryegrass and soft brome performed well in the short term, and Flecha tall fescue, several hardinggrass varieties and Berber orchardgrass worked well in the long term.

Increasing forage productivity in the Sierra foothill rangelands would help sustain the livestock industry as land availability shrinks and lease rates rise, but hardly any studies have been done on forage selections. From 2009 to 2014, in one of the first long-term and replicated studies of seeding Northern California's Mediterranean annual rangeland, we compared the cover of 22 diverse forages to determine their establishment and survivability over time. Among the annual herbs, forage brassica (Brassica napus L.) and chicory (Cichorium intybus L.) proved viable options. Among the annual grasses, soft brome (Bromus hordeaceus) and annual ryegrass (Lolium multiflorum) performed well. However, these species will likely require frequent reseeding to maintain dominance. Long-term goals of sustained dominant cover (> 3 years) are best achieved with perennial grasses. Perennial grasses that persisted with greater than 50% cover were Berber orchardgrass (Dactylis glomerata), Flecha tall fescue (Lolium arundinaceum) and several varieties of hardinggrass (Phalaris aquatica L., Perla koleagrass, Holdfast, Advanced AT). In 2014, these successful perennials produced over three times more dry matter (pounds per acre) than the unseeded control and also suppressed annual grasses and yellow starthistle (Centaurea solstitialis L.) cover.

A study of 10 California drylots on summer afternoons found diverse heat abatement strategies in place and a wide range of cow respiration rates.

California summers are hot, compromising the welfare and productivity of dairy cows. To minimize negative effects, producers use shade, fans and sprayed water. However, little is known about how those heat abatement strategies are provided in commercial conditions, nor their effectiveness. Ten dairies with drylots, a common housing system in California, were assessed for strategies provided, and the cows' responses to heat load were observed for 3 days in the afternoon. Dairies were diverse in all aspects. Shade varied in terms of placement (at corral and feed bunk or at corral only) and amount (28 to 74 square feet, or 2.6 to 6.9 square meters, per cow). The quantity of water used to spray cows ranged from 0 to 6.8 gallons (0 to 25.6 liters) per hour per cow. Across dairies, there was a range in the cows' shade use (47% to 98% of herd) and feeding activity (7% to 33% of herd). Respiration rates ranged from 65 (normal) to 95 breaths per minute (very hot) and were positively related to inactivity. Our results indicate that there are opportunities to improve cooling, and consequently dairy cattle welfare, in drylots.

Over 90% of the water applied to sites in Davis and Scott Valley percolated to recharge groundwater, making this a viable practice on highly permeable soils.

It is well known that California experiences dramatic swings in precipitation that are difficult to predict and challenging to agriculture. In times of drought, groundwater serves as a crucial savings account that is heavily relied upon. However, few tools exist to proactively refill this crucial reserve in wet years. We explored the idea of intentional winter flooding of agricultural land to promote on-farm recharge of the underlying groundwater. Field experiments were conducted on two established alfalfa stands to determine the feasibility of groundwater recharge and test realistic water application amounts and timings and potential crop damage. We studied soils with relatively high percolation rates and found that most of the applied water percolated to the groundwater table, resulting in short-lived saturated conditions in the root zone and minimal yield loss. While caution is appropriate to prevent crop injury, winter recharge in alfalfa fields with highly permeable soils appears to be a viable practice.

The slowdown in unauthorized Mexico–U.S. migration has set off a race in U.S. agriculture between rising imports, more machines, and foreign guest workers. Trade policy, including North American Free Trade Agreement (NAFTA) re-negotiations, and immigration policy, including more enforcement and new or revised guest worker programs, will determine the winner.

Focus groups with Yolo County farmers demonstrate that farmers' perceptions of and responses to the regulation are important to its success.

Agriculture is the largest human use of water in California, which gives farmers a critical role in managing water to meet the goals of the Sustainable Groundwater Management Act (SGMA). To explore farmers' perspectives on SGMA, we held focus groups with 20 farmers in Yolo County, where the groundwater basin has been given a high/medium priority under SGMA. The farmers had varying perspectives about the factors that led to SGMA and varying responses to the regulation. They suggested that drought, competing agricultural and urban uses, and an increase in perennial crops were factors in recent water use, resulting in changes to water quality and quantity. Impacts of those changes included variable well levels, increased infrastructure costs, and ecosystem impacts, which farmers had responded to by implementing multiple management strategies. Additional research in other regions is imperative to provide farmers' viewpoints and strategies to policymakers, irrigation districts, farmer cooperatives, and the agricultural industry and give farmers a voice at the table.

A review of wage data from agricultural employers suggests that most California farmworkers were employed for less than a full year in 2015.

The average employment of hired workers in California agriculture (NAICS 11) rose over 10% between 2005 and 2015, when some 16,400 agricultural establishments hired an average 421,300 workers who were paid a total of $12.8 billion, which was 27% of the state's $47 billion in farm sales. This means that a full-time equivalent (FTE) employee would earn $30,300, implying an hourly wage of $14.55 for 2,080 hours of work. We extracted all Social Security numbers reported by California agricultural establishments and found that the average annual pay received by the 848,000 workers who had at least one job on California farms was $20,500 in 2015, two-thirds of the average annual wage of an FTE worker, reflecting some combination of lower wages and less than full-year work.

Automated thinners were as accurate in thinning lettuce as manual thinning, produced comparable yields, and were more than three times faster than thinning crews.

Salinas Valley lettuce growers are adopting automated lettuce thinners to improve labor efficiency. We conducted field studies in 2014 and 2015 to compare the time involved in automated and manual thinning of direct-seeded lettuce and any differences in lettuce quality and yield. We recorded the number of doubles (two closely spaced plants) left behind after thinning, time taken to remove the doubles, final crop stand, efficiency in weed removal, crop yield and disease incidence. Using an automated thinner in place of manual hoeing reduced the thinning labor requirement from 7.31 ± 0.5 person-hours per acre to 2.03 ± 0.5 person-hours per acre. Automated thinning left more doubles than manual thinning, resulting in additional time to remove them, but was overall more labor-efficient and had no impact on yield or disease incidence.

Over 90% of the water applied to sites in Davis and Scott Valley percolated to recharge groundwater, making this a viable practice on highly permeable soils.

It is well known that California experiences dramatic swings in precipitation that are difficult to predict and challenging to agriculture. In times of drought, groundwater serves as a crucial savings account that is heavily relied upon. However, few tools exist to proactively refill this crucial reserve in wet years. We explored the idea of intentional winter flooding of agricultural land to promote on-farm recharge of the underlying groundwater. Field experiments were conducted on two established alfalfa stands to determine the feasibility of groundwater recharge and test realistic water application amounts and timings and potential crop damage. We studied soils with relatively high percolation rates and found that most of the applied water percolated to the groundwater table, resulting in short-lived saturated conditions in the root zone and minimal yield loss. While caution is appropriate to prevent crop injury, winter recharge in alfalfa fields with highly permeable soils appears to be a viable practice.

Focus groups with Yolo County farmers demonstrate that farmers' perceptions of and responses to the regulation are important to its success.

Agriculture is the largest human use of water in California, which gives farmers a critical role in managing water to meet the goals of the Sustainable Groundwater Management Act (SGMA). To explore farmers' perspectives on SGMA, we held focus groups with 20 farmers in Yolo County, where the groundwater basin has been given a high/medium priority under SGMA. The farmers had varying perspectives about the factors that led to SGMA and varying responses to the regulation. They suggested that drought, competing agricultural and urban uses, and an increase in perennial crops were factors in recent water use, resulting in changes to water quality and quantity. Impacts of those changes included variable well levels, increased infrastructure costs, and ecosystem impacts, which farmers had responded to by implementing multiple management strategies. Additional research in other regions is imperative to provide farmers' viewpoints and strategies to policymakers, irrigation districts, farmer cooperatives, and the agricultural industry and give farmers a voice at the table.